1. Field of the Invention
This invention relates, generally, to the arts of robotics and neuroscience. More particularly, it relates to a system for studying human grasping techniques by simultaneously identifying the contact position and orientation of the fingertip and measuring the force and torque exerted by the fingertip during various predetermined grasps.
2. Description of the Prior Art
Understanding of local mechanical interactions between human fingertips and an object is crucial to understanding human dexterity. With various kinds of force sensors, the fingertip force at the contact points on an object may be measured to study human dexterous grasping and manipulation. Many robot grasp planning and control algorithms have been developed with inspirations from human grasping studies. However, models that simply include contact force and contact location on the object have limited utility.
Studying human grasping techniques has significant implications for robotics because a human hand exhibits some of the most complex human motor skills. Many studies have proposed various taxonomies of human grasping. A basic distinction is between a power grasp, where the goal is to stabilize an object to resist external forces, and a precision grasp, which is an essential skill for manipulating an object, maintaining the grasp during various tasks, and re-grasping.
A preponderance of research has focused on precision grasps and on instrumentation to measure the fingertip forces and position on the object during contact. A rich experimental paradigm for the study of human grasping was disclosed by Johansson and Westling in Roles of Glabrous Skin Receptors and Sensorimotor Memory in Automatic Control of Precision Grip when Lifting Rougher or More Slippery Objects. This approach to studying human grasping involves parallel force-sensing pads for opposition grasps between the index finger and the thumb. This approach has been generalized to add more touch pads to include the middle, ring, and little fingers in addition to the index finger-thumb pair. In general, instrumented objects are typically created that incorporate miniature 6-axis force/torque sensors at predefined grasp points.
Besides the complex hand postures and forces during grasping, the great variance in what parts of the fingertip contact an object makes the grasping studies very complex. Many studies have been carried out to characterize the mechanical profile in the fingertip responding to a force. For example, Serina et al. and Pawluk and Howe have examined the dynamic force response of the fingertip to indenters of different sizes and shapes.
Many research teams have experimented with using various kinds of force sensors to measure the fingertip force at the contact points on an object. Many encouraging results have been achieved. However, more and more researchers have realized the limitation of the models that only include contact force and contact position on the object. Many researchers have sought for a way to measure the contact position on the fingertip to better model and understand more sophisticated grasping techniques such as rolling and re-grasping.
Commercial tactile sensors and flexible tactile sensors have been successfully embedded on many robotic fingers to provide rich spatial grasping information for grasping control. However, due to their stiffness, those tactile sensors cannot deform along with the human finger tissue to preserve the elastic profile, which prevents them from being used in many human grasping studies. Most studies attach tactile sensors on the force sensors rather than on the fingertip, thus obtaining local contact spatial profiles around the contact point, but not being capable of identifying the contact position on the fingertip.
Thus there is a need in neuroscience and robotics for a sensor capable of measuring the fingertip force and torque, the contact location, and the orientation of the fingertip.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the needed structure could be provided.